mesa: Make ARB_gpu_shader5 core-profile-only

Requires GLSL 1.50 or higher, which we only support in the core profile.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
i965: Enable ARB_gpu_shader5 on Gen7

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
docs: Mark off ARB_gpu_shader5 for i965

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
docs: Update relnotes for ARB_gpu_shader5, sort list

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>